The Best Fertilizer for Japanese Red Maples

A Japanese maple provides bright color in a yard.

The Japanese maple (Acer palmatum) is a deciduous shade and ornamental tree with at least 19 known cultivars that display red and crimson colors. The Sherwood Flame cultivar matures at about 10 feet tall and has reddish purple leaves in spring and summer, and the Autumn Glory cultivar reaches 10 to 25 feet tall and gains its crimson color in fall. Japanese maples grow well in U.S. Department of Agriculture plant hardiness zones 5 to 8 and are simple to maintain if their soil is kept moist.

Need for Fertilizer

Mature Japanese maples do not always need to be fertilized because they have an extensive root system. Watch for changes in growth patterns from year to year. If a tree's twigs grow fewer than 6 inches in a year, or its leaves are smaller than normal, then fertilization may benefit the tree. Dropping all of the leaves before autumn is another indication that fertilizer may be needed. Japanese maples regularly change leaf color throughout the growing season. Although that is an indication of nutrient deficiency in other trees, it should not be used alone in determining whether or not a Japanese maple needs to be fertilized. Overfertilization can cause root damage that will exacerbate the observed problems. Do not fertilize newly planted Japanese maple trees until after their first year in their new location. After the first year, young trees can be fertilized regularly for the first three years to promote development of their root system.

Type of Fertilizer

Complete fertilizers contain varying amounts of nitrogen, phosphorous and potassium. Nitrogen is the most important component for increasing twig and leaf growth, and phosphorous and potassium are involved in photosynthesis and other processes. Slow-release fertilizers that are appropriate for Japanese maples have about three times more nitrogen than phosphorous. The nutrient ratios are listed on a fertilizer package labels. A product labeled with a 16-4-8 ratio contains 16 percent nitrogen, 4 percent phosphorous and 8 percent potassium. This means that a 10 pound bag of 16-4-8 fertilizer has a total of 1.6 pounds of nitrogen in the entire bag.

Amount of Fertilizer

Base the amount of fertilizer to use on the amount of nitrogen that is required. A general guideline to use for mature Japanese maple trees is 1/10 pound of nitrogen for every 1 inch of tree trunk diameter measured at 4 1/2 feet from the ground. If you fertilize other plants in the Japanese maple trees' area at the same time, use the guideline of 1/10 pound of nitrogen per 100 square feet. The trees will take advantage of lawn fertilizer; so do not re-apply fertilizer to areas of a yard that have been treated.

Location for Fertilizer

The root system of a Japanese maple tree may extend 4 feet into the soil, but the majority of the feeder roots responsible for absorbing nutrients are in the top 12 inches of soil. Spreading fertilizer on the soil surface is sufficient to reach these feeder roots. Spread fertilizer evenly around each tree, beginning at least 1 foot from its trunk and extending to at least 1 1/2 times the diameter of the tree's canopy. If the soil is compacted or subject to excessive water runoff, the fertilizer can be applied in a series of holes 6 to 8 inches deep in the same area with about five holes per 1 inch of trunk diameter.

About the Author

Joshua Bush has been writing from Charlottesville, Va., since 2006, specializing in science and culture. He has authored several articles in peer-reviewed science journals in the field of tissue engineering. Bush holds a Ph.D. in chemical engineering from Texas A&M University.